DIELECTRIC-CONSTANTS OF GE, SN, AND ISOELECTRONIC SEMICONDUCTORS

Static dielectric constants of Ge, Sn, and isoelectronic semiconductor s are calculated by using the full f-sum rule including all possible t ransitions of d band electrons. The d band effect on the dielectric co nstant is expressed by using a newly defined D factor different from t he empirical D factor introduced by Van Vechten. The new D factor is d irectly expressed in terms of the average band gap, the energy of the d band, and the coupling oscillator strength between valence and d ban ds so that it has a well defined meaning in contrast to the empirical D factor. The calculated D values well reproduce the observed dielectr ic constant and the effective number of valence electrons which repres ents the excess deviation from the usual valence electron number.